Urgency is the most abused lever in e-commerce. Fake countdown timers and permanent "almost gone" badges have trained customers to ignore scarcity claims. Which is exactly why real, data backed urgency works so well: when the message says 14 units left and the product page agrees, the customer believes it, and belief converts.
True Urgency Has Two Inputs
The first input is the stock level itself, delivered by Shopify's inventory webhook the moment a product crosses its low stock threshold. The second, and the one most setups skip, is velocity: how fast the product is currently selling. Twenty units left selling two per week is not urgent. Twenty units selling eight a day is a 60 hour window. Calculating days of inventory remaining at current velocity is what separates an honest urgency campaign from a boy who cried sellout.
The Segment Is the Other Half
Blasting "only X left" to the full list wastes the signal on people who never cared about the product. The automated version pulls the segment with demonstrated intent: subscribers who viewed the product in the last 30 days without buying, plus cart abandoners, matched at the variant level. Those people get the email immediately, and the ones who don't open within 24 hours get an SMS follow up. Conversions are attributed to the event, so the store learns which products and thresholds actually respond to urgency.
The low stock engine, including the webhook setup and segment logic, is the second of three pipelines documented on our inventory driven marketing engine page, between the overstock clearance engine and the trending amplification engine.